Equine herpesvirus type 1 (EHV-1) causes abortion and respiratory infection that are extremely dangerous health risk for domestic horses of all ages and categories, as well as for other members of Equidae family. Only certain strains of EHV-1 cause encephalitis.
Vaccination of horses with live attenuated or inactivated vaccines against EHV-1 is commonly practiced using commercial vaccine products. In the USA, there are currently eight commercial vaccines that are manufactured by four veterinary biological manufacturers. The vaccines are produced to contain a single strain of EHV-1, multiple strain of EHV-1, combination of both EHV-1 and equine herpesvirus type 4 (EHV-4) available, or combination of EHV-1, EHV-4, and equine influenza virus subtypes type 1 and 2. Those vaccines are, in general, effective against respiratory infection although the duration of immunity is short and frequent immunization is required. Several attempts to identify and vaccinate against equine herpes are described in U.S. Pat. Nos. 6,544,526; 6,395,283; 6,248,333; 6,225,111; 6,193,983; and 6,083,511; which are hereby incorporated herein by reference.
However, none of those vaccines have been tested for protection of horses against neurologic disease caused by EHV-1. Clinical evidence indicates that immunization of horses with those marketed vaccines do not provide protection against neurologic disease caused by the neurotropic strains of EHV-1. During the EHV-1 outbreak in Findlay, Ohio, which occurred in January 2003, eighty-eight percent (119/135) of previously well-vaccinated horses were clinically affected with mild upper respiratory disease and/or fever, indicating the horses were protected against the clinical respiratory disease caused by EHV-1. However, over forty horses developed neurological signs. Among them, 12 horses died or were euthanized due to the severe neurological disease.
A vaccine composed of a neurotropic strain of EHV-1 or its component alone or in combination with other strains of EHV-1 may be used to provide protection against EHV-1 infection and neurologic disease caused by the neurotropic strain of EHV-1. Thus, a vaccine that contains a neurotropic stain of EHV-1 or its component and will overcome the drawback of the commercial vaccine and protect equine species against neurologic disease in addition to respiratory infection and abortion caused by EHV-1. It would be likely that the most appropriate vaccine uses a strain of virus derived from a neurotropic strain of EHV-1 for the protection of horses against neurologic disease as well as other clinical diseases caused by the virus. Here, we describe our invention of a vaccine against infection and neurologic disease caused by EHV-1.